1. Field of the Invention
The present invention relates to a switching power supply apparatus used as a direct-current power source in an electronic appliance.
2. Description of the Prior Art
A conventionally known example of such a switching power supply apparatus is disclosed, for example, in Japanese Patent Application Laid-Open No. H10-304658. The switching power supply apparatus disclosed in this publication is provided with a main switch that turns on and off a direct current applied to the primary coil of a transformer, a secondary-side rectifying/smoothing circuit that rectifies and smoothes the on/off signal induced in the secondary coil of the transformer so as to supply it as a main output signal, a subsidiary power source that rectifies and smoothes the on/off signal induced in the bias coil of the transformer so as to supply it as a subsidiary supply voltage, an error amplifier that generates an error voltage signal that represents the difference between the subsidiary supply voltage output from the subsidiary power source and a reference voltage, and a comparator that feeds the main switch with an on/off control signal in such a way as to reduce the error voltage signal output from the error amplifier. This switching power supply apparatus is further provided with a light-load switching controller portion that temporarily stops the on/off operation of the main switch when the main output voltage becomes higher than an upper limit voltage and that restarts the on/off operation of the main switch when the main output voltage becomes lower than a lower limit voltage.
In this conventional switching power supply apparatus, control is so performed that the on/off operation of the main switch is temporarily stopped when the main output voltage output from the secondary-side rectifying/smoothing circuit becomes higher than the upper limit voltage, and that the on/off operation of the main switch is restarted when the main output voltage becomes lower than the lower limit voltage.
Here, however, while the on/off operation of the main switch is temporarily stopped when the main output voltage becomes higher than the upper limit voltage, operating power is kept supplied to the individual circuits and control devices provided in the control circuit that drives and controls the main switch. This causes wasteful power loss. Specifically, in a configuration where the on/off operation of the main switch is temporarily stopped when the main output voltage output from the secondary-side rectifying/smoothing circuit becomes higher than the upper limit voltage and the on/off operation of the main switch is restarted when the main output voltage becomes lower than the lower limit voltage, i.e., in so-called burst switching control, the operating power is kept supplied to all the circuits and control devices provided in the control circuit even while the switching operation is being stopped. This causes wasteful consumption of the supply current, resulting in wasteful power loss.
Also in the conventional switching power supply apparatuses disclosed in Japanese Patent Applications Laid-Open Nos. 2001-346378 and 2002-58238, as in the switching power supply apparatus described above, even during the period in which the switching operation of the main switch is being stopped in burst switching control, the operating power is kept supplied to all the circuits and control devices provided in the switching signal controlling circuit. This causes wasteful consumption of the supply current, resulting in wasteful power loss.
Incidentally, in the conventional switching power supply apparatus disclosed in Japanese Patent Application Laid-Open No. 2001-86745, to reduce power consumption in a stand-by state, the switching operation of the main switching device is stopped in that state. Thus, the aim of this invention is not to reduce the power loss suffered while the switching operation of the main switching device is being stopped in burst switching control.